Some automotive fuels may exhibit rapid evaporation in response to diurnal variations in ambient temperature. Emissions resulting from such vapors may be reduced in automotive applications via evaporative emission control systems (EVAP), The EVAP systems include a fuel vapor storage canister containing adsorbent, such as carbon, that traps those fuel vapors and feeds them back to the vehicle's engine for combustion during canister purging operations, thus, reducing evaporative emissions from the vehicle and improving fuel economy.
In a canister purge operation, a canister purge valve (CPV) coupled between the engine intake and the fuel canister may be duty cycled, allowing for intake manifold vacuum to be applied to the fuel canister. On a boosted engine, that vacuum draw may be supplied via an ejector during boosted operation. Simultaneously, a canister vent valve coupled between the fuel canister and atmosphere can be opened, allowing for fresh air to enter the canister. Further, in some examples, a fuel tank isolation valve coupled between the fuel tank and the fuel canister may be closed to reduce the flow of fuel vapors from the fuel tank to the engine. This configuration facilitates desorption of stored fuel vapors from the adsorbent material in the canister, regenerating the adsorbent material for further fuel vapor adsorption.
However, there may be circumstances where the CPV may become degraded, such that the CPV does not effectively seal. Such an issue may result in engine manifold vacuum being undesirably communicated to the evaporative emissions system and a fuel system of the vehicle during engine operation. CPV degradation may result from, for example, carbon pellets, dust, fibers, etc., becoming associated with the CPV such that sealing effectiveness becomes degraded. In such occurrences where CPV degradation is determined, an onboard diagnostic trouble code (DTC) may set, which may include a request to have the vehicle serviced which is undesirable from a customer standpoint. Similar issues may be seen for a fuel tank pressure control valve (TPCV), which, like the CPV may be duty cycled during particular vehicle operating conditions to depressurize the fuel tank, whereby fuel vapors released from the fuel tank may be routed to the engine for combustion.
The inventors have herein recognized the above-mentioned issues, and have developed systems and methods to at least partially address them. In one example, a method comprises in response to an indication that a valve that regulates an amount of fuel vapor routed to an engine of a vehicle has degraded sealing, timing opening and closing events of the valve to coincide with higher than a threshold pressure differences across the valve as compared to lower than the threshold pressure differences in terms of pressure oscillations across the valve, the pressure oscillations stemming from an intake of the engine. In this way, issues related to degradation of the valve may be mitigated without having to have the vehicle serviced by a technician.
In one example of the method, the method may further comprise mapping the pressure oscillations including a frequency, a phase and an amplitude of the pressure oscillations across the valve based on one or more of at least an engine speed, an engine load, a timing of opening and/or closing of intake and/or exhaust valves of the engine, and an ambient temperature. In some example, the method may include relying on feedback from a pressure sensor positioned at the valve in order to map the pressure oscillations. In another example of the method, the method may additionally or alternatively comprise mapping the pressure oscillations via output from a pressure sensor positioned upstream of the valve, and another pressure sensor positioned downstream of the valve.
In another example of the method, timing the opening and the closing events of the valve to coincide with the higher than the threshold pressure differences across the valve takes place during a purging operation of a fuel vapor storage canister that routes the fuel vapor to the engine. In such an example, timing the opening and the closing events of the valve to coincide with the higher than the threshold pressure differences across the valve may serve to clean the valve. In such an example, the valve comprises a canister purge valve positioned in a purge conduit that couples the fuel vapor storage canister to the engine.
In another example of the method, timing the opening and the closing events of the valve to coincide with the higher than the threshold pressure differences across the valve takes place during a fuel tank depressurization operation where a fuel tank of the vehicle is depressurized. In such an example, timing the opening and the closing events of the valve to coincide with the higher than the threshold pressure differences across the valve may serve to clean the valve. In such an example, the valve comprises a fuel tank pressure control valve positioned in a conduit that couples the fuel tank to an evaporative emissions system of the vehicle.
In another example, the engine may be combusting air and fuel during timing the opening and the closing events of the valve to coincide with the higher than the threshold pressure differences across the valve.
In another example, the method may further comprise, subsequent to timing opening and closing events of the valve to coincide with higher than a threshold pressure differences across the valve as compared to lower than the threshold pressure differences in terms of pressure oscillations across the valve, scheduling a follow-up test diagnostic to ascertain whether the valve no longer exhibits the degraded sealing.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.